Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$134.74	9.164%	$147.0876	$147.09	$147.10	$147.10
Purchase #2	$41.75	12.697%	$47.051	$47.05	$47.05	$47.10
Purchase #3	$31.89	12.497%	$35.8753	$35.88	$35.90	$35.90
Purchase #4	$99.87	5.314%	$105.1771	$105.18	$105.20	$105.20
Purchase #5	$248.83	4.697%	$260.5175	$260.52	$260.50	$260.50
Purchase #6	$38.56	13.826%	$43.8913	$43.89	$43.90	$43.90
Purchase #7	$233.42	8.566%	$253.4148	$253.41	$253.40	$253.40
7 purchase totals =	$829.06		$893.0146	$893.02	$893.05	$893.10